Nonaqueous electrolyte secondary battery and secondary battery module

ABSTRACT

The present disclosure relates to a secondary battery module including a nonaqueous electrolyte secondary battery and an elastic body. The elastic body has a compressive elastic modulus of 5 MPa to 120 MPa. The nonaqueous electrolyte secondary battery includes a positive electrode and a negative electrode. The positive electrode includes a positive electrode collector containing Ti as a main component and having a thickness of 1 μm to 8 μm. The negative electrode includes a first layer and a second layer sequentially formed from a side with the negative electrode collector. The first layer contains negative electrode active material particles containing first carbon-based active material particles with a 10% proof stress of 3 MPa or less. The second layer contains negative electrode active material particles containing second carbon-based active material particles with a 10% proof stress of 5 MPa or greater.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2020-046791 filed on Mar. 17, 2020, which is incorporated herein byreference in its entirety including the specification, claims, drawings,and abstract.

TECHNICAL FIELD

The present disclosure relates to a technique for a nonaqueouselectrolyte secondary battery and to a secondary battery module.

BACKGROUND

A nonaqueous electrolyte secondary battery, such as a lithium ionsecondary battery, typically includes an electrode body and electrolyte.The electrode body includes a positive electrode having a positiveelectrode active material layer and a negative electrode having anegative electrode active material layer, in which these electrodes arelaminated via a separator. Such a nonaqueous electrolyte secondarybattery is, for example, a battery to be charged or discharged withcharge carriers (for example, lithium ions) in the electrolyte movingback and forth between the respective electrodes.

For example, Patent Document 1 describes use of a negative electrode ina nonaqueous electrolyte secondary battery, the negative electrodeincluding a negative electrode collector and a negative electrode activematerial layer, in which the negative electrode active material layerincludes a first layer and a second layer sequentially formed from aside with the negative electrode collector, the first layer includesfirst carbon-based active material particles with a 10% proof stress of3 MPa or less, and the second layer includes second carbon-based activematerial particles with a 10% proof stress of 5 MPa or greater.According to Patent Document 1, use of the negative electrode activematerial layer including the above-mentioned first layer and secondlayer enables provision of a nonaqueous electrolyte secondary batterysuperior in output characteristics.

CITATION LIST Patent Literature

-   Patent Document 1: WO 2019/187537 A1

SUMMARY

As a safety evaluation test for evaluating the tolerance of a batteryagainst internal short-circuiting, for example, a nailing test isavailable in which a battery is stabbed with a nail to simulateoccurrence of internal short-circuiting to observe the amount of heatgeneration of the battery for safety evaluation of the battery. As for anonaqueous electrolyte secondary battery including a negative electrodeactive material layer having a laminated structure including a firstlayer and a second layer, as is described in Patent Document 1, there isroom for improvement, in that the amount of heat generation in thebattery in a nailing test can be reduced, although drop in output of abattery in a charge/discharge cycle is prevented.

In view of the above, it is an object of the present disclosure toreduce the amount of heat generation of a battery in a nailing test, aswell as to prevent drop in output of a battery in a charge/dischargecycle, with respect to a nonaqueous electrolyte secondary battery and asecondary battery module, each including a negative electrode activematerial layer having a laminated structure including a first layer anda second layer.

According to one aspect of this disclosure, there is provided asecondary battery module, including at least one nonaqueous electrolytesecondary battery, and an elastic body disposed together with thenonaqueous electrolyte secondary battery, for receiving a load from thenonaqueous electrolyte secondary battery in a direction in which thenonaqueous electrolyte secondary battery and the elastic body aredisposed, wherein the nonaqueous electrolyte secondary battery includesan electrode body including a laminate of a positive electrode, anegative electrode, and a separator disposed between the positiveelectrode and the negative electrode, and an enclosure for storing theelectrode body therein, the elastic body has a compressive elasticmodulus of 5 MPa to 120 MPa, the positive electrode includes a positiveelectrode collector containing Ti as a main component and having athickness of 1 μm to 8 μm, the negative electrode includes a negativeelectrode collector and a negative electrode active material layerincluding a first layer and a second layer sequentially formed from aside with the negative electrode collector, and the first layer containsnegative electrode active material particles containing firstcarbon-based active material particles with a 10% proof stress of 3 MPaor less, and the second layer contains negative electrode activematerial particles containing second carbon-based active materialparticles with a 10% proof stress of 5 MPa or greater.

According to another aspect of this disclosure, there is provided anonaqueous electrolyte secondary battery, including an electrode bodyincluding a laminate of a positive electrode, a negative electrode, anda separator disposed between the positive electrode and the negativeelectrode, an elastic body for receiving a load from the electrode bodyin a lamination direction of the electrode body, and an enclosure forstoring the electrode body and the elastic body therein, wherein theelastic body has a compressive elastic modulus of 5 MPa to 120 MPa, thepositive electrode includes a positive electrode collector containing Tias a main component and having a thickness of 1 μm to 8 μm, the negativeelectrode includes a negative electrode collector and a negativeelectrode active material layer including a first layer and a secondlayer sequentially formed from a side with the negative electrodecollector, the first layer contains negative electrode active materialparticles containing first carbon-based active material particles with a10% proof stress of 3 MPa or less, and the second layer containsnegative electrode active material particles containing secondcarbon-based active material particles with a 10% proof stress of 5 MPaor greater.

According to one aspect of the present disclosure, it is possible toreduce the amount of heat generation of a battery in a nailing test, aswell as to prevent drop in output of a battery in a charge/dischargecycle.

BRIEF DESCRIPTION OF DRAWINGS

Embodiment(s) of the present disclosure will be described based on thefollowing figures, wherein:

FIG. 1 is a perspective view of a secondary battery module according toan embodiment;

FIG. 2 is an exploded perspective view of the secondary battery moduleaccording to the embodiment;

FIG. 3 is a schematic cross sectional view of the nonaqueous electrolytesecondary battery in expansion;

FIG. 4 is a schematic cross sectional view illustrating the condition ofan electrode body in a nailing test;

FIG. 5 is a schematic cross sectional view of an elastic body disposedin an enclosure;

FIG. 6 is a schematic perspective view of a cylindrical windingelectrode body;

FIG. 7 is a schematic cross sectional view of a negative electrode;

FIG. 8 is a schematic perspective view of one example of an elasticbody; and

FIG. 9 is a schematic cross sectional view of a part of an elastic bodyheld between an electrode body and an enclosure.

DESCRIPTION OF EMBODIMENTS

One example of an embodiment will now be described in detail. Thedrawings to be referred to in description of the embodiment are onlyschematically illustrated, and the dimensions and ratios of thestructural components illustrated in the drawings may differ from thoseof the corresponding actual components.

FIG. 1 is a perspective view of a secondary battery module according toan embodiment. FIG. 2 is an exploded perspective view of the secondarybattery module according to the embodiment. A secondary battery module 1includes, as one example, a stacked body 2, a pair of binding members 6,and a cooling plate 8. The stacked body 2 includes a number ofnonaqueous electrolyte secondary batteries 10, a number of insulationspacers 12, a number of elastic bodies 40, and a pair of end plates 4.

Each nonaqueous electrolyte secondary battery 10 is, for example, achargeable/dischargeable secondary battery, such as a lithium ionsecondary battery. A nonaqueous electrolyte secondary battery 10 in thisembodiment is a so-called rectangular battery, and includes an electrodebody 38 (refer to FIG. 3), electrolyte, and a flat rectangularparallelepiped enclosure 13. The enclosure 13 includes an outer can 14and a sealing plate 16. The outer can 14 has a substantially rectangularopening on its one surface, so that the electrode body 38, theelectrolyte, and so forth are inserted into the outer can 14 through theopening. The outer can 14 is desirably coated with an insulation film,not illustrated, such as a shrink tube. To the opening of the outer can14, the sealing plate 16 is provided to cover the opening to therebyseal the outer can 14. The sealing plate 16 constitutes a first surface13 a of the enclosure 13. The sealing plate 16 is connected to the outercan 14, for example, by means of laser, friction stir joining, orbrazing.

The enclosure 13 may be a cylindrical case, for example, and may be anouter body made of a laminated sheet including a metal layer and a resinlayer.

The electrode body 38 has a structure including a number of sheetpositive electrodes 38 a and a number of sheet negative electrodes 38 balternately laminated via separators 38 d (refer to FIG. 3).Specifically, the positive electrode 38 a, the negative electrode 38 b,and the separator 38 d are laminated in a first direction X. That is,the first direction X corresponds to the lamination direction of theelectrode body 38. The electrodes disposed at the respective end sidesof the electrode body 38 in the lamination direction are opposed to therespective longer lateral surfaces, to be described later, of theenclosure 13. Note that the illustrated first direction X, a seconddirection Y, and a third direction Z are directions orthogonal to oneanother.

The electrode body 38 may be a cylindrical winding electrode body formedby winding a laminate including a band-shaped positive electrode and aband-shaped negative electrode laminated via a separator. Alternatively,the electrode body 38 may be a flat winding electrode body formed byflattening a cylindrical winding electrode body. For a flat windingelectrode body, a rectangular parallelepiped outer can is usable, whilefor a cylindrical winding electrode body, a cylindrical outer can isdesirably used.

On the sealing plate 16; that is, on the first surface 13 a of theenclosure 13, an output terminal 18 for electrical connection to thepositive electrode 38 a of the electrode body 38 is formed at a positioncloser to one end in the longitudinal direction, and an output terminal18 for electrical connection to the negative electrode 38 b of theelectrode body 38 is formed at a position closer to the other end. Notethat the output terminal 18 for connection to the positive electrode 38a will be hereinafter referred to as a positive electrode terminal 18 a,and the output terminal 18 for connection to the negative electrode 38 bas a negative electrode terminal 18 b. In the case where no polaritydistinction between the pair of output terminals 18 is necessary, thepositive electrode terminal 18 a and the negative electrode terminal 18b will be collectively referred to as output terminals 18.

The outer can 14 has a bottom surface opposed to the sealing plate 16.In addition, the outer can 14 has four lateral surfaces connecting theopening and the bottom surface. Two out of the four lateral surfaces area pair of longer lateral surfaces connected to two respective opposedlonger edges of the opening. Each longer lateral surface is a surfacehaving the largest area, or the main surface, among the surfaces of theouter can 14. Each longer lateral surface is a lateral surface expandingin a direction intersecting the first direction X (for example, beingorthogonal). Meanwhile, the two lateral surfaces other than the twolonger lateral surfaces are a pair of shorter lateral surfaces connectedto the respective shorter edges of the opening and those of the bottomsurface of the outer can 14. The bottom surface, the longer lateralsurfaces, and the shorter lateral surfaces of the outer can 14respectively correspond to the bottom surface, the longer lateralsurfaces, and the shorter lateral surfaces of the enclosure 13.

In the description of this embodiment, for convenience, the firstsurface 13 a of the enclosure 13 is defined as the upper surface of thenonaqueous electrolyte secondary battery 10. In addition, the bottomsurface of the enclosure 13 is defined as the bottom surface of thenonaqueous electrolyte secondary battery 10; the longer lateral surfacesof the enclosure 13 as the longer lateral surfaces of the nonaqueouselectrolyte secondary battery 10; and the shorter lateral surfaces ofthe enclosure 13 as the shorter lateral surfaces of the nonaqueouselectrolyte secondary battery 10. As to the secondary battery module 1,the surface on a side of the upper surface of the nonaqueous electrolytesecondary battery 10 is defined as the upper surface of the secondarybattery module 1; the surface on a side of the bottom surface of thenonaqueous electrolyte secondary battery 10 as the bottom surface of thesecondary battery module 1; and the surfaces on the respective sides ofthe shorter lateral surfaces of the nonaqueous electrolyte secondarybattery 10 as the lateral surfaces of the secondary battery module 1. Inaddition, the direction toward the upper surface of the secondarybattery module 1 is defined as the upward direction in the verticaldirection; and the direction toward the bottom surface of the secondarybattery module 1 as the downward direction in the vertical direction.

The number of nonaqueous electrolyte secondary batteries 10 are alignedin parallel at predetermined intervals such that the longer lateralsurfaces of the adjacent nonaqueous electrolyte secondary batteries 10are opposed to each other. In this embodiment, the output terminals 18of the respective nonaqueous electrolyte secondary battery 10 aredisposed directed in the same direction, although these may be disposeddirected in different directions.

Two adjacent nonaqueous electrolyte secondary batteries 10 are disposed(stacked) such that the positive electrode terminal 18 a of onenonaqueous electrolyte secondary battery 10 is disposed adjacent to thenegative electrode terminal 18 b of the other nonaqueous electrolytesecondary battery 10, and the positive electrode terminal 18 a and thenegative electrode terminal 18 b are serially connected to each othervia a busbar (not illustrated). Alternatively, the output terminals 18of the same polarity of the number of adjacent nonaqueous electrolytesecondary batteries 10 may be connected in parallel via a busbar tothereby form a nonaqueous electrolyte secondary battery block, and thenonaqueous electrolyte secondary battery blocks may be seriallyconnected to each other.

The insulation spacer 12 is disposed between two adjacent nonaqueouselectrolyte secondary batteries 10 for electrical insulation between thetwo nonaqueous electrolyte secondary batteries 10. The insulation spacer12 is made of insulation resin, for example. Examples of the resin forformation of the insulation spacer 12 include polypropylene,polybutylene terephthalate, and polycarbonate. The number of nonaqueouselectrolyte secondary batteries 10 and the number of insulation spacers12 are alternately stacked. The insulation spacer 12 is disposed alsobetween the nonaqueous electrolyte secondary battery 10 and the endplate 4.

The insulation spacer 12 includes a planar portion 20 and a wall portion22. The planar portion 20 intervenes between the opposed longer lateralsurfaces of two adjacent nonaqueous electrolyte secondary batteries 10.This arrangement ensures insulation between the outer cans 14 of theadjacent nonaqueous electrolyte secondary batteries 10.

The wall portion 22 extends from the outer edge of the planar portion 20in a direction in which the nonaqueous electrolyte secondary batteries10 are aligned, and covers a part of the upper surface, the lateralsurface, and a part of the bottom surface of the nonaqueous electrolytesecondary battery 10. This ensures some distance, for example, betweenthe adjacent nonaqueous electrolyte secondary batteries 10 or between anonaqueous electrolyte secondary battery 10 and the end plate 4 on thelateral side. The wall portion 22 has a notch 24 where the bottomsurface of the nonaqueous electrolyte secondary battery 10 is exposed.In addition, the insulation spacer 12 has an urging force receivingportion 26 formed upward on each end portion of the insulation spacer 12in the second direction Y.

The elastic bodies 40 are disposed in the first direction X togetherwith the number of nonaqueous electrolyte secondary batteries 10. Thatis, the first direction X is the lamination direction of the electrodebody 38, as described above, and also a direction in which thenonaqueous electrolyte secondary batteries 10 and the elastic bodies 40are disposed, or a disposition direction. The elastic body 40 is shapedlike a sheet, and intervenes, for example, between the longer lateralsurface of each nonaqueous electrolyte secondary battery 10 and theplanar portion 20 of each insulation spacer 12. The elastic body 40,disposed between two adjacent nonaqueous electrolyte secondary batteries10, may be one sheet or a laminate including a number of sheetslaminated. The elastic body 40 may be secured on the surface of theplanar portion 20 with adhesive agent or the like. Alternatively, arecess may be formed on the planar portion 20, so that the elastic body40 may be fit in the recess. Still alternatively, the elastic body 40and the insulation spacer 12 may be formed integrally. Stillalternatively, the elastic body 40 may serve also as the planar portion20.

The number of nonaqueous electrolyte secondary batteries 10, insulationspacers 12, and elastic bodies 40, which are aligned in parallel to oneanother, are held between the pair of end plates 4 in the firstdirection X. Each end plate 4 is made of a metal plate or a resin plate,for example. Each end plate 4 has a screw hole 4 a that penetrates theend plate 4 in the first direction X, so that a screw 28 is insertedinto the screw hole 4 a.

Each of the pair of binding members 6 is a longitudinal member whoselongitudinal direction corresponds to the first direction X. The pair ofbinding members 6 are disposed opposed to each other in the seconddirection Y. Between the pair of binding members 6, the stacked body 2is disposed. Each binding member 6 includes a main portion 30, a supportportion 32, a number of urging portions 34, and a pair of fixtureportions 36.

The main portion 30 is a rectangular portion extending in the firstdirection X. The main portion 30 extends parallel to the lateralsurfaces of the respective nonaqueous electrolyte secondary batteries10. The support portion 32 extends in the first direction X, andprojects in the second direction Y from the lower end of the mainportion 30. The support portion 32 is a plate member continuing in thefirst direction X, and supports the stacked body 2.

The number of urging portions 34 are connected to the upper end of themain portion 30, and project in the second direction Y. The supportportion 32 is opposed to the urging portion 34 in the third direction Z.The number of urging portions 34 are disposed at predetermined intervalsin the first direction X. Each of the urging portions 34 has a leafspring shape, for example, and urges the nonaqueous electrolytesecondary batteries 10 toward the support portion 32.

Each of the pair of fixture portions 36 is a plate member formed on therespective end portion of the main portion 30 in the first direction Xand projecting in the second direction Y. The pair of fixture portions36 are opposed to each other in the first direction X. Each fixtureportion 36 has a through hole 36 a for insertion of a screw 28therethrough. The pair of fixture portions 36 have the binding member 6secured to the stacked body 2.

The cooling plate 8 is a mechanism for cooling the number of nonaqueouselectrolyte secondary batteries 10. The stacked body 2, being bundledwith the pair of binding members 6, is placed on the main surface of thecooling plate 8, and secured onto the cooling plate 8 with a fasteningmember (not illustrated), such as a screw, penetrating a through hole 32a of the support portion 32 and a through hole 8 a of the cooling plate8.

FIG. 3 is a schematic cross sectional view of nonaqueous electrolytesecondary batteries in expansion. In FIG. 3, a lower number ofnonaqueous electrolyte secondary batteries 10 than the number of thenonaqueous electrolyte secondary batteries 10 actually provided areillustrated; the inside structure of the nonaqueous electrolytesecondary battery 10 is illustrated more simply; and the insulationspacer 12 is not illustrated. As illustrated in FIG. 3, each nonaqueouselectrolyte secondary battery 10 incorporates the electrode body 38 (thepositive electrode 38 a, the negative electrode 38 b, and the separator38 d). The outer can 14 of the nonaqueous electrolyte secondary battery10 expands and shrinks due to expansion and shrinkage of the electrodebody 38 through charging and discharging. Once the outer can 14 of eachnonaqueous electrolyte secondary battery 10 expands, a load G1 directedoutward in the first direction X is applied to the stacked body 2. Thatis, the elastic body 40, disposed together with the nonaqueouselectrolyte secondary battery 10, receives a load directed in the firstdirection (or the disposition direction of the nonaqueous electrolytesecondary battery 10 and the elastic body 40, which is also thelamination direction of the electrode body 38) from the nonaqueouselectrolyte secondary battery 10. Meanwhile, a load G2 corresponding tothe load G1 is applied to the stacked body 2 by the end plate 4.

FIG. 4 is a schematic cross sectional view of an electrode body in anailing test. As illustrated in FIG. 4, the positive electrode 38 aincludes a positive electrode collector 50 and a positive electrodeactive material layer 52 formed on the positive electrode collector 50,while the negative electrode 38 b includes a negative electrodecollector 54 and a negative electrode active material layer 56 formed onthe negative electrode collector 54. Note that the negative electrodeactive material layer 56 includes a first layer 56 a and a second layer56 b sequentially formed from a side with the negative electrodecollector 54, as to be described later (refer to FIG. 7). As illustratedin FIG. 4, when a nonaqueous electrolyte secondary battery is stabbedwith a nail 58 in a nailing test until the nail 58 fully penetrates thepositive electrode 38 a and the separator 38 d to reach the negativeelectrode 38 b, internal short-circuiting is caused, and a short-circuitcurrent flows. This leads to heat generation in the nonaqueouselectrolyte secondary battery.

Note here that the positive electrode collector 50 in this embodiment isa Ti-containing positive electrode collector that contains Ti as a maincomponent and has a thickness of 1 μm to 8 μm. Such a positive electrodecollector that contains Ti as a main component is highly readily fusiblewhen a short-circuit current flows, as compared with a positiveelectrode collector that contains Al as a main component, for example.Hence, the period of time after occurrence of internal short-circuitinguntil fusing of the positive electrode collector 50 in nailing test isshortened. Note that the thickness of a positive electrode collectorcontaining Ti as a main component is preferably within theabove-mentioned range, in view of formation of a positive electrode.

The elastic body 40 in this embodiment is an elastic body having acompressive elastic modulus of 5 MPa to 120 MPa. Since such an elasticbody having a compressive elastic modulus of 5 MPa to 120 MPa modifiesthe load G1 directed outward in the first direction X and the load G2corresponding to the load G1, excessive approach between the positiveelectrode 38 a and the negative electrode 38 b is prevented. Thisprevents increase in area of a short-circuited portion of the positiveelectrode collector 50 (a portion of the positive electrode collectorthat is in direct contact with a nail) in a nailing test, as comparedwith a case in which the above-mentioned Ti-containing positiveelectrode collector is used but an elastic body with a compressiveelastic modulus of 5 MPa to 120 MPa is not disposed or an elastic bodywith a compressive elastic modulus in excess of 120 MPa is disposed.Hence, the period of time after occurrence of internal short-circuitinguntil fusing of the positive electrode collector 50 is further shortenedin a nailing test. Note here that a nonaqueous electrolyte secondarybattery including the negative electrode active material layer 56 havinga laminated structure including the first layer 56 a and the secondlayer 56 b, to be described later, prevents drop in output of a batteryin a charge/discharge cycle, but still causes large heat generation dueto a large short-circuiting current when internal short-circuitingoccurs in a nailing test. In such a nonaqueous electrolyte secondarybattery 10 as well, use of the elastic body 40 having theabove-mentioned compressive elastic modulus and the positive electrodecollector 50 having the above-mentioned thermal conductive rate shortensthe period of time after occurrence of internal short-circuiting untilfusing of the positive electrode collector 50 in a nailing test, andthus reduces the amount of heat generation in a nailing test.

FIG. 5 is a schematic cross sectional view of an elastic body that isdisposed inside an enclosure. The elastic body 40 is not necessarilydisposed along with the nonaqueous electrolyte secondary battery 10, asdescribed above; that is, disposed outside the enclosure 13, but can bedisposed inside the enclosure 13. The elastic body 40 illustrated inFIG. 5 is disposed on each end side of the electrode body 38 in thelamination direction (the first direction X) of the electrode body 38,and held between the inside wall of the enclosure 13 and the electrodebody 38.

When the electrode body 38 expands through charging and discharging ofthe nonaqueous electrolyte secondary battery 10, a load directed outwardin the first direction X is generated in the electrode body 38. That is,the elastic body 40 inside the enclosure 13 receives a load directed inthe first direction (the lamination direction of the electrode body 38)from the electrode body 38. Hence, provided that the elastic body 40 hasa compressive elastic modulus of 5 MPa to 120 MPa, and the positiveelectrode collector 50 is a Ti-containing positive electrode collectorthat contains T1 as a main component and has a thickness in the range of1 μm to 8 μm, the same operational effect as that described above can beobtained.

The elastic body 40 in the enclosure 13 can be disposed anywhere,provided that the elastic body 40 can receive a load from the electrodebody 38 in the lamination direction of the electrode body 38. Forexample, in the case where the electrode body 38 is a cylindricalwinding electrode body 38 illustrated in FIG. 6, for example, theelastic body 40 may be disposed at a winding core portion 39 of thecylindrical winding electrode body 38. Note that the laminationdirection of the cylindrical winding electrode body 38 corresponds tothe diameter direction (R) of the electrode body 38. As the electrodebody 38 expands or shrinks, a load directed in the lamination direction(the diameter direction (R) of the electrode body 38) is generated withrespect to the electrode body 38, and the elastic body 40 inside thewinding core portion 39 receives the load in the lamination direction ofthe electrode body 38. In the case where a number of electrode bodies 38are disposed inside the enclosure 13, which is not described byreference to the drawings, the elastic body 40 may be disposed betweenadjacent electrode bodies 38. In the case of a flat winding electrodebody 38 as well, an elastic body may be similarly disposed at the middleof the electrode body.

The positive electrode 38 a, the negative electrode 38 b, the separator38 d, the elastic body 40, and the electrolyte will now be described indetail.

The positive electrode 38 a includes the positive electrode collector50, and the positive electrode active material layer 52 formed on thepositive electrode collector 50.

The positive electrode collector 50 is a positive electrode collectorthat contains Ti as a main component and has a thickness of 1 μm to 8μm. Containing Ti as a main component means that the Ti content of thepositive electrode collector 50 is 50 wt % or greater. The Ti content ofthe positive electrode collector 50 is preferably 75 wt % or greater,for example, in view of facilitating fusing of the positive electrodecollector 50, and more preferably is 90 wt % or greater. The positiveelectrode collector 50 may contain an element other than Ti. Examples ofsuch an element include Fe, Si, N, C, O, and H, in which the respectivepreferred contents are, for example, 0.01% to 0.2% for Fe, 0.011 to0.02% for Si, 0.001% to 0.02% for N, 0.001% to 0.02% for C, 0.04% to0.14% for O, and 0.003% to 0.01% for H. The thickness of the positiveelectrode collector 50 is preferably 2 μm to 7 μm, and more preferablyis 3 μm to 6 μm, for example, in view of facilitating fusing of thepositive electrode collector 50, increase of the expansion rate of thepositive electrode collector 50 to prevent possible separation of thepositive electrode active material layer 52, or enhancement ofmechanical strength.

The positive electrode active material layer 52 contains a positiveelectrode active material. The positive electrode active material layer52 preferably contains an electrically conductive material and a bindingagent, besides the positive electrode active material. The positiveelectrode active material layer 52 is preferably formed on therespective surfaces of the positive electrode collector 50.

Examples of a usable positive electrode active material include lithiumtransition metal composite oxides. Examples of the metal elementcontained in the lithium transition metal composite oxides include Ni,Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta,and W. Among these, at least one of Ni, Co, and Mn is preferablycontained. Examples of the composite oxide include a lithium transitionmetal composite oxide containing Ni, Co, and Mn, and a lithiumtransition metal composite oxide containing Ni, Co, and Al. Lithiumtransition metal composite oxide may contain a lithium nickel-containingcomposite oxide that contains Ni by 70 mol % to 100 mole % relative tothe total amount of metal elements other than Li, for example, in viewof high capacity of a battery. The percentage of Ni contained in thelithium nickel-containing composite oxide is preferably in the range of70 mol % to 100 mol % relative to the total amount of metal elementsother than Li, for example, in view of high capacity of a nonaqueouselectrolyte secondary battery. The percentage is more preferably in therange of 80 mol % to 98 mol %, and further preferably in the range of 82mol % to 89 mol %. The lithium nickel-containing composite oxide ispreferably contained in the positive electrode active material in anamount of 80 wt % or greater, for example, in view of high capacity of anonaqueous electrolyte secondary battery, and more preferably iscontained in an amount of 90 wt % or greater.

Examples of the electrically conductive member include carbonaceousmaterials, such as carbon black, acetylene black, Ketjen black, andgraphite. Examples of the binding agent include fluorine resins, such aspolytetrafluoroethylene (PTFE), and polyvinylidene difluoride (PVdF),polyacrylonitrile (PAN), polyimide resins, acrylic resins, andpolyolefin resins. These resins may be used together with, for example,cellulose derivatives, such as carboxymethyl cellulose (CMC) or saltsthereof, or polyethylene oxide (PEO).

The positive electrode 38 a can be formed, for example, by applying apositive electrode mixture slurry containing a positive electrode activematerial, an electrically conductive material, and a binding agent ontothe positive electrode collector 50, then drying and rolling theresultant coating film to thereby form a positive electrode activematerial layer 52 on the positive electrode collector 50. The positiveelectrode collector 50 is formed to have a thickness in the range of 1μm to 8 μm to improve the extension rate of the positive electrodecollector 50. This leads to a small difference in extension rate betweenthe positive electrode active material layer 52 and the positiveelectrode collector 50 when rolling is applied in formation of thepositive electrode 38 a, which can prevent separation of the positiveelectrode active material layer 52 from the positive electrode collector50.

FIG. 7 is a schematic cross sectional view of a negative electrode. Asillustrated in FIG. 7, the negative electrode 38 b includes the negativeelectrode collector 54, and the negative electrode active material layer56 including the first layer 56 a and the second layer 56 b sequentiallyformed from a side with the negative electrode collector 54. For thenegative electrode collector 54, foil of a metal that is stable in thepotential range of the negative electrode 38 b or a film having themetal disposed on its front layer is used. Examples of the materialinclude copper. The negative electrode active material layer 56 (thefirst layer 56 a and the second layer 56 b) is preferably formed on therespective surfaces of the negative electrode collector 54.

The first layer 56 a contains negative electrode active materialparticles P1, while the second layer 56 b contains negative electrodeactive material particles P2. The first layer 56 a and the second layer56 b preferably contain a binding agent, for example. Examples of thebinding agent include the same binding agent as that contained in thepositive electrode active material layer 52. The thickness of thenegative electrode active material layer 56 is, for example, 20 μm to120 μm on one side of the negative electrode collector 54. The thicknessof the first layer 56 a is preferably 30 to 80% that of the negativeelectrode active material layer 56, and more preferably is 50 to 70%.The thickness of the second layer 56 b is preferably 20 to 70% that ofthe negative electrode active material layer 56, and more preferably is30 to 50%. Note that the negative electrode active material layer 56 isnot limited to those which include solely the first layer 56 a and thesecond layer 56 b, but may additionally include a third layer.

The negative electrode 38 b is made, for example, using a first negativeelectrode mixture slurry containing negative electrode active materialparticles P1 and a binding agent, and a second negative electrodemixture slurry containing negative electrode active material particlesP2 and a binding agent. Specifically, the first negative electrodemixture slurry is applied to a surface of the negative electrodecollector 54, and the resultant coating film is dried. Thereafter, thesecond negative electrode mixture slurry is applied onto the firstcoating film made of the first negative electrode mixture slurry, andthe resultant second coating film is dried. This provides the negativeelectrode 38 b having the negative electrode active material layer 56including the first layer 56 a and the second layer 56 b, formed on thenegative electrode collector 54.

The negative electrode active material particles P1 contained in thefirst layer 56 a contain first carbon-based active material particleswith a 10% proof stress of 3 MPa or less (hereinafter referred to ascarbon-based active material particles A). Meanwhile, the negativeelectrode active material particles P2 contained in the second layer 56b contain second carbon-based active material particles with a 10% proofstress of 5 MPa or greater (hereinafter referred to as carbon-basedactive material particles B). The carbon-based active material particlesA, B are particles made of carbonaceous material, and preferably containgraphite as a main component. Examples of the graphite include naturalgraphite, such as flaky graphite, lump graphite, and earthy graphite,and artificial graphite, such as lump artificial graphite andgraphitized mesophase carbon microbeads.

The carbon-based active material particles A are soft particles with a10% proof stress of 3 MPa or less. Meanwhile, the carbon-based activematerial particles B are hard particles with a 10% proof stress of 5 MPaor greater. Forming the negative electrode 38 b so as to have alaminated structure including the second layer 56 b containing thecarbon-based active material particles B disposed on a side closer tothe surface of the negative electrode 38 b and the first layer 56 acontaining the carbon-based active material particles A disposed on aside closer to the negative electrode collector 54 prevents, forexample, disconnection of the electrically conductive path of thenegative electrode active material layer 56, and, moreover, increasespermeability of the electrolyte into the negative electrode activematerial layer 56. Hence, it is expected that drop in output of abattery in a charge/discharge cycle is prevented.

Note that, in this specification, a 10% proof stress refers to a stresscaused when carbon-based active material particles A, B are compressedby 10 vol %. A 10% proof stress is measurable with respect to onecarbon-based active material particles A, B with a micro compressiontesting machine (MCT-211 manufactured by Shimazu Corporation) or thelike. For the measurement, particles each having a particle diameterequal to the particle diameter D5 of each carbon-based active materialparticles A, B are used.

Although the carbon-based active material particles A may containsubstantially no amorphous component (amorphous carbon), thecarbon-based active material particles B preferably contain amorphouscomponent. Specifically, the carbon-based active material particles Bmay contain amorphous component in an amount of 1 to 5 wt %. In thiscase, a 10% proof stress of 5 MPa or greater can be readily obtained.The amount of amorphous component contained in the carbon-based activematerial particles A is, for example, 0.1 to 2 wt %, and is preferablysmaller than that in the carbon-based active material particles B.

The amorphous component (amorphous carbon) consists of carbon atoms inwhich a graphite crystalline structure does not develop; that is, carbonatoms in the state of an amorphous or microcrystal random layerstructure. Specifically, the amorphous component refers to a componentwhose d (002) lattice spacing by X-ray diffraction is 0.342 nm orgreater. Specific examples of the amorphous component include hardcarbon (hardly graphitizable carbon), soft carbon (easily graphitizablecarbon), carbon black, carbon fiber, and activated carbon. The amorphouscomponent is obtained through carbonization treatment with resin orresin composition, for example. Examples of raw materials usable in theamorphous component are phenolic thermoset resins, thermoplastic resinssuch as polyacrylonitrile, and petroleum-based or coal-derived tar orpitch.

An amorphous component is preferably present in a state adhering onto asurface of a graphite-based carbon. Note here that being adhering refersto being chemically and/or physically bonded, and to a state in whichamorphous component is not released from a surface of the graphite-basedcarbon when the active material particles are agitated in water ororganic solvent. The physical properties of the amorphous component andthe amount of adhering amorphous component are adjustable, for example,by changing the kind and/or amount of the raw material (such aspetroleum-based or coal-derived tar or pitch), and/or the temperature ator a period of time of carbonization treatment with the raw material.

In view of readiness in obtaining a 10% proof stress of 5 MPa orgreater, for example, the carbon-based active material particles B arepreferably particles each including a core portion having voids, and ashell portion disposed covering the core portion. The core portiondesirably has a structure consisting of graphite and amorphous carbonand having voids inside. The shell portion preferably has a structureconsisting of amorphous carbon and having a thickness of 50 nm orgreater. The weight ratio of the core portion and the shell portion isdesirably 99:1 to 95:5. The porosity of the shell portion is preferablylower than that of the core portion. That is, the porosity of the coreportion is desirably 1 to 5%, while that of the shell portion is 0.01 to1%.

For example, the core portion is formed by mixing graphite and agraphitable binder, then heating the mixture to 500 to 3000° C. under aninert gas atmosphere or a nonoxidizing atmosphere, and applyingpowder-forming, such as crushing, cracking, sorting, spheroidizing, tothe carbonized material. Examples of the graphite include naturalgraphite and artificial graphite. The average partial diameter of thegraphite is preferably 10 μm or less, more preferably 5 μm or less.Examples of the graphitable binder include coal-derived,petroleum-based, or artificial pitch and tar, thermoplastic resins, andthermoset resins. For void formation, addition of an additive with a lowresidual carbon rate is preferred. Graphite and binder can be mixed atany ratio without limitation, while the ratio between the residualcarbon of the binder component and the graphite is preferably 1:99 to30:70. For example, a shell portion can be formed, for example, using aCVD method with acetylene or methane, or a manner of mixing coal pitch,petroleum pitch, phenol resins, or the like, and the carbonaceousmaterial of the core portion before thermal treatment. Theabove-described formation method can readily provide carbon-based activematerial particles with a 10% proof stress of 5 MPa or greater.

The negative electrode active material particles P1 contained in thefirst layer 56 a may include carbon-based active material particles B,besides the carbon-based active material particles A, or any negativeelectrode active materials other than the carbon-based active materialparticles A, B, within a range not impairing the object of thisdisclosure. The content of the carbon-based active material particles Ain the first layer 56 a is desirably 50 wt % or greater, for example,relative to the total amount of the negative electrode active materialparticles P1. In addition, the negative electrode active materialparticles P2 contained in the second layer 56 b may include carbon-basedactive material particles A besides the carbon-based active materialparticles B, or any other negative electrode active materials besidesthe carbon-based active material particles A, B, in a range notimpairing the object of the present disclosure. The content of thecarbon-based active material particles B in the second layer 56 b isdesirably 50 wt % or greater, for example, relative to the total amountof the negative electrode active material particles P2.

Examples of the negative electrode active materials other than thecarbon-based active material particles A, B include metals that arealloyed with lithium, such as silicon (Si), tin (Sn), for example, oralloys or compounds that contain metal elements, such as Si, Sn, or thelike. Among these, in view of high capacity of a battery, compoundscontaining Si are preferred. In the case where the negative electrodeactive material layer 56 contains negative electrode active materialsother than the carbon-based active material particles A, B, the contentof the negative electrode active materials other than the carbon-basedactive material particles A, B preferably holds “the first layer 56a>the second layer 56 b” in view of prevention of drop in output of abattery in a charge/discharge cycle, and the second layer 56 bpreferably contains substantially no such materials.

A preferred compound containing Si is an Si oxide, expressed as SiO_(x)(0.5<=x<=1.6), for example. An Si oxide expressed as SiO_(x) has astructure, for example, in which Si microparticles are dispersed in anamorphous Sift matrix. Further, the compound containing Si may be acompound expressed as Li_(2y)SiO_((2+y)) (0<y<2) with Si microparticlesdispersed in a lithium silicate phase.

It is preferred that an electrically conductive film made of highlyelectrically conductive material is formed on the surface of theparticles of the compound containing Si. Examples of the material of theelectrically conductive film include at least one kind of materialselected from among carbonaceous materials, metals, and metal compounds.Among these, carbonaceous materials such as amorphous carbon arepreferred. A carbon film can be formed, for example, using a CVD methodusing acetylene or methane, for example, or a manner of mixing coalpitch, petroleum pitch, phenol resins, or the like, and a silicon-basedactive material before thermal treatment. Alternatively, an electricallyconductive filler, such as carbon black, may be adhered on the surfaceof the particles of a compound containing Si with a binding agent tothereby form an electrically conductive film.

The negative electrode active material particles P2 contained in thesecond layer 56 b preferably have a BET specific surface area smallerthan that of the negative electrode active material particles P1contained in the first layer 56 a. This improves, for example,permeability of the electrolyte into the negative electrode activematerial layer 56 and retention therein, which in some cases preventsdrop in output of a battery in a charge/discharge cycle. The BETspecific surface area of the negative electrode active materialparticles P2 is preferably 0.5 m²/g or greater to less than 3.5 m²/g,for example, and more preferably is 0.75 m²/g or greater to 1.9 m²/g orless. Further, the BET specific surface area of the negative electrodeactive material particles P1 is preferably 3.5 m²/g or greater to 5 m²/gor less, and more preferably is 2.5 m²/g or greater to 4.5 m²/g or less.BET specific surface area is measured with a BET method, using aconventionally known specific surface area measuring device (forexample, Macsorb (registered trademark) HM model-1201 manufactured byMountech Co., Ltd.).

The porosity of the second layer 56 b is preferably greater than that ofthe first layer 56 a. This improves permeability of the electrolyte intothe negative electrode active material layer 56 and retention therein,for example, which in some cases prevents drop in output of a battery ina charge/discharge cycle.

Note here that the porosities of the first layer 56 a and the secondlayer 56 b are two-dimensional values obtained based on the percentageof the area of the voids between the respective particles in each layerrelative to the cross sectional area of the layer, and can be obtainedfollowing the procedure below, for example.

(1) A part of a negative electrode is cut off, and treated with an IonMilling System (for example, IM4000 manufactured by Hitachi High-TechCorporation) to expose a cross section of the negative electrode activematerial layer 56.(2) Using a scanning electron microscope, a backscattered electron imageof the cross section of the first layer 56 a of the exposed negativeelectrode active material layer 56 is captured.(3) The image of the cross section captured as above is taken into acomputer, and binarized with an image analysis software (for example,ImageJ prepared by National Institutes of Health) to obtain a binarizedimage in which the cross sections of the particles in the crosssectional image are colored black and those of the voids betweenparticles are colored white.(4) To obtain the porosity of the first layer 56 a, the area of thevoids between the particles in a measurement range (for example, 50μm×50 μm) is calculated from the binarized image. Assuming that themeasurement area as a cross sectional area (2500 μm²=50 μm×50 μm) of thefirst layer 56 a, the porosity of the first layer 56 a (the area of thevoids between particles×100/the cross sectional area of the negativeelectrode active material layer 56) is calculated from the calculatedarea of the voids between the particles. The porosity of the secondlayer 56 b is similarly measured.

Examples of a method for adjusting the porosities of the first layer 56a and the second layer 56 b include a method for adjusting a rollingforce to be applied to the first coating film and the second coatingfilm in formation of the negative electrode active material layer 56.

As the separator 38 d, for example, a porous sheet having ionpermeability and insulation is used. Specific examples of the poroussheet include porous thin films, woven fabrics, and nonwoven fabrics.Examples of materials usable in the separator 38 d include olefine-basedresins, such as polyethylene and polypropylene, and cellulose. Theseparator 38 d may be a laminate including a cellulose fiber layer and athermoplastic resin fabric layer, such as olefine-based resins.Alternatively, the separator 38 d may be a multiple layer separatorincluding a polyethylene layer and a polypropylene layer. The surface ofthe separator 38 d may be coated with such a material as aramid-basedresins, ceramic, or the like.

Examples of raw materials usable in the elastic body 40 are thermosetelastomers, such as natural rubbers, urethane rubbers, silicone rubbers,and fluorine rubbers, and thermoplastic elastomers, such as polystyrene,olefin, polyurethane, polyester, and polyamide. These materials may befoamed. Other examples include heat insulators carrying a spongiosemember, such as silica xerogel.

In this embodiment, it is preferred that the compressive elastic moduliof the negative electrode active material layer 56, the separator 38 d,and the elastic body 40 are defined as follows. That is, preferably, thecompressive elastic modulus of the separator 38 d is lower than that ofthe negative electrode active material layer 56, and that of the elasticbody 40 is lower than that of the separator 38 d. That is, thecompressive elastic moduli hold the relationship “the negative electrodeactive material layer 56>the separator 38 d>the elastic body 40”. Thus,among the above-mentioned, the negative electrode active material layer56 is least easily deformable, while the elastic body 40 is most readilydeformable. Defining the compressive elastic moduli of the respectivemembers as described above improves permeability of the electrolyte intothe negative electrode active material layer 56 and retainment therein,which in some cases prevents drop in output of a battery in acharge/discharge cycle. The compressive elastic modulus of the separator38 d is preferably, for example, a compressive elastic modulus 0.3 to0.7 times as that of the negative electrode active material layer 56,and more preferably 0.4 to 0.6 times. The compressive elastic modulus ofthe elastic body 40 is within the range of 5 MPa to 120 MPa, andpreferably is within the range of 25 MPa to 100 MPa.

The compressive elastic modulus is calculated by dividing the deformedamount of a sample in the thickness direction upon application of apredetermined load to the sample in the thickness direction, by acompressed area, and then multiplying by the thickness of the sample.That is, the compressive elastic modulus is calculated with anexpression of “compressive elastic modulus (MPa)=load (N)/compressedarea (mm²)×(deformed amount of a sample (mm)/thickness of the sample(mm))”. Note that in measurement of the compressive elastic modulus ofthe negative electrode active material layer 56, the compressive elasticmodulus of the negative electrode collector 54 is measured, and thecompressive elastic modulus of the negative electrode 38 b including thenegative electrode active material layer 56 formed on the negativeelectrode collector 54 is measured. Then, based on the compressiveelastic moduli of the negative electrode collector 54 and the negativeelectrode 38 b, the compressive elastic modulus of the negativeelectrode active material layer 56 is calculated. Alternatively, in thecase where the compressive elastic modulus of the negative electrodeactive material layer 56 is obtained from the formed negative electrode38 b, the compressive elastic modulus of the negative electrode 38 b ismeasured; the compressive elastic modulus of the negative electrodecollector 54, or the remaining when the negative electrode activematerial layer 56 is taken off from the negative electrode 38 b, ismeasured; and the compressive elastic modulus of the negative electrodeactive material layer 56 is calculated, based on these measuredcompressive elastic moduli.

Examples of a method for adjusting the compressive elastic modulus ofthe negative electrode active material layer 56 include a method foradjusting the rolling force to be applied to the negative electrodemixture slurry formed on the negative electrode collector 54.Alternatively, for example, changing the material and physicalproperties of the negative electrode active material enables adjustmentof the compressive elastic modulus of the negative electrode activematerial layer 56. Note that adjustment of the compressive elasticmodulus of the negative electrode active material layer 56 is notlimited to the above-described method. The compressive elastic modulusof the separator 38 d is adjusted, for example, through selection of thematerial, control of the pore rate and/or opening diameter of thematerial, or the like, while the compressive elastic modulus of theelastic body 40 is adjusted, for example, through selection of thematerial and control of the shape of the material.

The elastic body 40 may have a consistent compressive elastic modulusover its one surface. Alternatively, the elastic body 40 may have astructure in which easiness of deformation varies over a surface, as tobe described later.

FIG. 8 is a schematic perspective view of one exemplary elastic body.The elastic body 40 illustrated in FIG. 8 includes a soft portion 44 anda hard portion 42. The hard portion 42 is positioned closer to the outeredge of the elastic body 40 than is the soft portion 44. The elasticbody 40 illustrated in FIG. 8 has a structure in which the hard portion42 is disposed on each end of the elastic body 40 in the seconddirection Y, and the soft portion 44 is disposed between the two hardportions 42. The soft portion 44 is preferably disposed overlapping themiddle portion of the longer lateral surface of the enclosure 13 whenviewed in the first direction X, and also the middle portion of theelectrode body 38. The hard portion 42 is preferably disposedoverlapping the outer edge of the longer lateral surface of theenclosure 13, and also the outer edge of the electrode body 38.

As described above, the nonaqueous electrolyte secondary battery 10expands mainly due to expansion of the electrode body 38. Specifically,the electrode body 38 expands to a large degree in a portion closer toits middle. That is, the electrode body 38 is displaced a greaterdistance in the first direction at a position closer to its middle, anda smaller distance at a position further outward from the middle towardthe outer edge. Following this displacement of the electrode body 38,the nonaqueous electrolyte secondary battery 10 is displaced a greaterdistance in the first direction X in a position closer to the middle ofthe longer lateral surface of the enclosure 13, and a smaller distancein a position more outward from the middle of the longer lateral surfaceof the enclosure 13 toward the outer edge of the longer lateral surfaceof the enclosure 13. Thus, in the case where the elastic body 40illustrated in FIG. 8 is disposed inside the enclosure 13, the elasticbody 40 can receive a larger load generated due to large displacement ofthe electrode body 38 with the soft portion 44, and a smaller loadgenerated due to small displacement of the electrode body 38 with thehard portion 42. Further, in the case where the elastic body 40illustrated in FIG. 8 is disposed outside the enclosure 13, the elasticbody 40 can receive a large load generated due to large displacement ofthe nonaqueous electrolyte secondary battery 10 with the soft portion44, and a small load generated due to small displacement of thenonaqueous electrolyte secondary battery 10 with the hard portion 42.

The elastic body 40 illustrated in FIG. 8 includes a recessed portion 46that is recessed in the first direction X, leaving a non-recessedportion adjacent to the recessed portion 46. The non-recessed portioncan be partially displaced toward the recessed portion 46 upon receiptof a load from the nonaqueous electrolyte secondary battery 10 or theelectrode body 38. That is, formation of the recessed portion 46 makesthe non-recessed portion readily deformable. In view of the above, inorder to make the soft portion 44 more readily deformable than the hardportion 42, it is preferred that the percentage in area of the recessedportion 46 occupied in the soft portion 44 when viewed in the firstdirection X is larger than that of the recessed portion 46 occupied inthe hard portion 42. Note that, although in the elastic body 40illustrated in FIG. 8 the recessed portion 46 is formed only in the softportion 44, the recessed portion 46 may be disposed in the hard portion42.

The recessed portion 46 includes a core portion 46 a and a number oflinear portions 46 b. The core portion 46 a is round and disposed at themiddle of the elastic body 40 when viewed in the first direction X. Thenumber of linear portions 46 b extend radially from the core portion 46a. The radially extending linear portions 46 b lead to a higherpercentage of the linear portions 46 b occupied in an area closer to thecore portion 46 a, leaving a smaller non-recessed portion there. Hence,the non-recessed portion is more readily deformable in an area closer tothe core portion 46 a.

The elastic body 40 may have a number of through holes that penetratethe elastic body 40 in the first direction X instead of, or in additionto, the above-mentioned recessed portion 46, which is not described byreference to drawings. Provision of such through holes can make aportion without such a through hole more readily deformable. Thus, inorder to make the soft portion 44 more readily deformable than the hardportion 42, it is preferred that the percentage in area of the throughholes occupied in the soft portion 44 when viewed in the first directionX is greater than that occupied in the hard portion 42.

Other examples of the elastic body will now be described.

FIG. 9 is a partial schematic cross sectional view of an elastic bodyheld between the electrode body and the enclosure. The elastic body 40receives a load from the electrode body 38 in the lamination direction(the first direction X) of the elastic body 38. The elastic body 40includes a base member 42 a where the hard portion 42 having apredetermined hardness is formed, and the soft portion 44 that is softerthan the hard portion 42. The hard portion 42 is a projecting portionprojecting from the base member 42 a toward the electrode body 38, andwill fracture or plastically deform upon receipt of a predetermined orlarger load. The soft portion 44 is shaped like a sheet, and disposed ata position closer to the electrode body 38 than is the base member 42 awhere the hard portion 42 is formed. The soft portion 44 is apart fromthe electrode body 38. The soft portion 44 has a through hole 44 a at aposition overlapping the hard portion 42 when viewed in the firstdirection X. The hard portion 42 is inserted into the through hole 44 asuch that the tip end of the hard portion 42 projects out of the softportion 44.

As the shape of the hard portion 42 changes, the elastic body 40 shiftsfrom a first state in which a load from the electrode body 38 isreceived with the hard portion 42 to a second state in which the load isreceived with the soft portion 44. That is, the elastic body 40initially receives a load in the lamination direction of the electrodebody 38, the load being generated due to expansion of the electrode body38, with the hard portion 42 (a first state). When the electrode body 38expands further due to some causes until application to the hard portion42 of a load that is too large for the hard portion 42 to receive, thehard portion 42 fractures or plastically deforms. Thereupon, theelectrode body 38 is brought into contact with the soft portion 44 tothereafter receive the load in the lamination direction of the electrodebody 38 (a second state).

In the case of an elastic body having concaves and convexes, thecompressive elastic modulus is calculated as “a compressive elasticmodulus (MPa)=a load (N)/a projection area of the elastic body in thesurface direction (mm²)×a deformed amount of the elastic body (mm)/thethickness (mm) of the convex portions of the elastic body)”.

The electrolyte is, for example, a nonaqueous electrolyte; that is, anorganic solvent (a nonaqueous solvent) containing supporting salt.Examples of the usable nonaqueous solvent include esters, ethers,nitriles, amides, or combination solvents of two or more kinds of these.Example of the supporting salt include lithium salts, such as LiPF₆.

EXAMPLES Experimental Example 1 [Formation of Positive Electrode]

As a positive electrode active material, a lithium nickel-containingcomposite oxide expressed as a general expressionLiNi_(0.85)Co_(0.06)Mn_(0.10)O₂ was used. This positive electrode activematerial, acetylene black, and polyvinylidene fluoride were mixed at asolid mass ratio of 97:2:1 to prepare a positive electrode mixtureslurry, using N-methyl-2-pyrrolidone (NMP) as a dispersion medium.

As a positive electrode collector, a Ti foil having a thickness of 5 μmwas used.

The above-mentioned positive electrode mixture slurry was applied toeach surface of the Ti foil, then dried, and rolled before being cutinto a predetermined size for an electrode. This provided a positiveelectrode having a positive electrode active material layer formed oneach surface of the positive electrode collector.

[Preparation of First Negative Electrode Mixture Slurry]

Graphite particles having a 10% proof stress of 2.1 MPa (carbon-basedactive material particles A), a dispersion of styrene-butadiene rubber(SBR), and sodium carboxymethyl cellulose (CMC-Na) were mixed at a solidmass ratio of 100:1:1 to prepare a first negative electrode mixtureslurry, using water as dispersion medium.

[Preparation of Second Negative Electrode Mixture Slurry]

Graphite particles having a 10% proof stress of 5.7 MPa (carbon-basedactive material particles B), a dispersion of styrene-butadiene rubber(SBR), and sodium carboxymethyl cellulose (CMC-Na) were mixed at a solidmass ratio of 100:1:1 to prepare a second negative electrode mixtureslurry, using water as a dispersion medium.

[Formation of Negative Electrode]

The first negative electrode mixture slurry was applied to each surfaceof a negative electrode collector made of a copper foil, then dried, androlled. Thereafter, the second negative electrode mixture slurry wasapplied onto the coating film, then dried, and rolled to thereby form anegative electrode active material layer including a first layer derivedfrom the first negative electrode mixture slurry and a second layerderived from the second negative electrode mixture slurry formed on thenegative electrode collector. The resultant body was cut into apredetermined size for an electrode, whereby a negative electrode wasobtained.

[Preparation of Electrolyte]

Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and dimethylcarbonate (DMC) were mixed at a volume ratio of 3:3:4. LiPF₆ wasdissolved in the mixed solvent at a density of 1.4 mol/L, wherebyelectrolyte was obtained.

[Formation of Nonaqueous Electrolyte Secondary Battery]

A negative electrode, a separator having a compressive elastic modulusof 130 MPa, and a positive electrode were laminated in this ordermultiple times to thereby form an electrode body. Then, the negativeelectrode and the positive electrode were connected to the positiveelectrode terminal and the negative electrode terminal, respectively.Thereafter, the result was stored inside an outer body made of analuminum laminate, the above-mentioned electrolyte was poured into theouter body, and the opening of the outer body was sealed, whereby anonaqueous electrolyte secondary battery was made.

The obtained nonaqueous electrolyte secondary battery was held by a pairof elastic bodies (foamed urethane having a compressive elastic modulusof 60 MPa), and then securely held by a pair of end plates, to therebymake a secondary battery module (with an elastic body). Further, theobtained nonaqueous electrolyte secondary battery was securely heldbetween a pair of end plates to thereby make a secondary battery module(without an elastic body).

Experimental Example 2

A secondary battery module with an elastic body and a secondary batterymodule without an elastic body were made in the same manner as inExperimental Example 1, except for use of graphite particles with a 10%proof stress of 6.6 MPa (carbon-based active material particles B) inpreparation of the second negative electrode mixture slurry.

Experimental Example 3

A secondary battery module with an elastic body and a secondary batterymodule without an elastic body were made in the same manner as inExperimental Example 1, except for use of graphite particles with a 10%proof stress of 27 MPa (carbon-based active material particles B) inpreparation of the second negative electrode mixture slurry.

Experimental Example 4

A secondary battery module with an elastic body and a secondary batterymodule without an elastic body were made in the same manner as inExperimental Example 1, except for use of a Ti foil having a thicknessof 1 μm as a positive electrode collector.

Experimental Example 5

A secondary battery module with an elastic body and a secondary batterymodule without an elastic body were made in the same manner as inExperimental Example 1, except for use of a Ti foil having a thicknessof 8 μm as a positive electrode collector.

Experimental Example 6

A secondary battery module with an elastic body and a secondary batterymodule without an elastic body were made in the same manner as inExperimental Example 1, except for use of a foamed urethane having acompressive elastic modulus of 40 MPa as an elastic body.

Experimental Example 7

A secondary battery module with an elastic body and a secondary batterymodule without an elastic body were made in the same manner as inExperimental Example 1, except for use of a foamed urethane having acompressive elastic modulus of 5 MPa as an elastic body.

Experimental Example 8

A secondary battery module with an elastic body and a secondary batterymodule without an elastic body were made in the same manner as inExperimental Example 1, except for use of a foamed urethane having acompressive elastic modulus of 120 MPa as an elastic body.

Experimental Example 9

A secondary battery module with an elastic body and a secondary batterymodule without an elastic body were made in the same manner as inExperimental Example 1, except for use of a separator having acompressive elastic modulus of 80 MPa and use of a foamed urethanehaving a compressive elastic modulus of 120 MPa as an elastic body.

Experimental Example 10

Although a secondary battery module was attempted to be made in the samemanner as in Experimental Example 1, except for use of a Ti foil havinga thickness of 10 μm as a positive electrode collector, as the positiveelectrode active material layer was separated from the positiveelectrode collector after rolling the coating film, a secondary batterymodule was not able to be made.

Experimental Example 11

A secondary battery module with an elastic body and a secondary batterymodule without an elastic body were made in the same manner as inExperimental Example 1, except for use a foamed urethane having acompressive elastic modulus of 130 MPa as an elastic body.

Experimental Example 12

A secondary battery module with an elastic body and a secondary batterymodule without an elastic body were made in the same manner as inExperimental Example 1, except for use of an Al foil having a thicknessof 12 μm as a positive electrode collector.

Experimental Example 13

A secondary battery module with an elastic body and a secondary batterymodule without an elastic body were made in the same manner as inExperimental Example 1, except for use of graphite particles with a 10%proof stress of 1.8 MPa (carbon-based active material particles B) inpreparation of the second negative electrode mixture slurry.

Experimental Example 14

A secondary battery module with an elastic body and a secondary batterymodule without an elastic body were made in the same manner as inExperimental Example 1, except for use of graphite particles with a 10%proof stress of 5.7 MPa (carbon-based active material particles A) inpreparation of the first negative electrode mixture slurry and use ofgraphite particles with a 10% proof stress of 27 MPa (carbon-basedactive material particles B) in preparation of the second negativeelectrode mixture slurry.

[Evaluation of Resistance Increase Rate in Charge/Discharge Cycle]

A secondary battery module with an elastic body in each experimentalexample was charged under a temperature condition of 25° C. with aconstant current of 0.5 It to half of the initial capacity. Then,charging of the secondary battery module was stopped and it was left asit was for fifteen minutes. Thereafter, the secondary battery module wascharged with a constant current of 0.1 It for ten seconds, and thevoltage after the charging was measured. Then, after the amount ofcharge corresponding to charging for ten seconds was discharged, thesecondary battery module was charged for ten seconds at a changedcurrent value, and the voltage after the charging was measured. Then,the amount of charge corresponding to charging for ten seconds wasdischarged. This charging, discharging, and voltage measurement wererepeated with a current at a value from 0.1 It to 2 It. Then, based onthe relationship between the measured voltage values and the currentvalue, a resistance value was obtained as a resistance value before acycle test.

A secondary battery module with an elastic body in each experimentalexample was given a charge/discharge cycle test under a conditionmentioned below to obtain a resistance value after 200 cycles, using theabove mentioned method, and an increase rate of the resistance valueafter 200 cycles relative to the resistance value before the cycle testwas calculated. A lower increase rate of the resistance value indicatesthat drop in output of a battery in the charge/discharge cycle wasfurther prevented.

A secondary battery module was given constant current charging under atemperature condition of 25° C. with a constant current of 0.5 It untilthe battery voltage became 4.2 V, and then given constant voltagecharging at 4.2 V until the current value became 1/50 It. Thereafter,the secondary battery module was given constant current discharge with aconstant current of 0.5 It until the battery voltage became 2.5 N. Thischarge/discharge cycle was repeated 200 times.

[Evaluation of Heat Generation Temperature of Battery in Nailing Test]

A secondary battery module in each experimental example was adjusted tobe in the state of charge (SOC) of 100% under a temperature condition of25° C. Then, the secondary battery module was stabbed with a needle witha radius of 0.5 mm and curvature φ of the tip end portion of 0.9 mm at aspeed of 0.1 mm/sec in the thickness direction of the nonaqueouselectrolyte secondary battery such that the positive electrodecommunicated with the negative electrode to thereby cause internalshort-circuiting. Then, the temperature on the surface of the batteryafter elapse of one minute after occurrence of internal short-circuitingwas measured.

Table 1 shows the physical properties of the positive electrodecollectors, the separators, the elastic bodies, and the negativeelectrode active material layers (first layers and second layers) usedin the respective experimental examples, and the evaluation results ofthe respective experimental examples.

TABLE 1 NEGATIVE HEAT ELASTIC BODY ELECTRODE ACTIVE RESISTANCEGENERATION SEPARATOR COMPRES- MATERIAL LAYER INCREASE TEMPERATUREPOSITIVE COMPRES- SIVE SECOND FIRST RATE IN OF BATTERY IN ELECTRODE SIVEELASTIC LAYER LAYER CHARGE/ NAILING TEST (° C.) COLLECTOR ELASTICMODULUS 10% PROOF 10% PROOF DISCHARGE WITHOUT WITH MATE- THICK- MODULUS(MPa) STRESS STRESS CYCLE ELASTIC ELASTIC RIAL NESS (μm) (MPa) (MPa)(MPa) (%) BODY BODY EXPERIMENTAL Ti 5 130 60 5.7 2.1 +12% 175 147EXAMPLE 1 EXPERIMENTAL Ti 5 130 60 6.6 2.1  +4% 176 150 EXAMPLE 2EXPERIMENTAL Ti 5 130 60 27 2.1  +3% 180 160 EXAMPLE 3 EXPERIMENTAL Ti 1130 60 5.7 2.1 +12% 178 156 EXAMPLE 4 EXPERIMENTAL Ti 8 130 60 5.7 2.1+12% 173 154 EXAMPLE 5 EXPERIMENTAL Ti 5 130 40 5.7 2.1 +12% 173 137EXAMPLE 6 EXPERIMENTAL Ti 5 130 5 5.7 2.1 +12% 174 132 EXAMPLE 7EXPERIMENTAL Ti 5 130 120 5.7 2.1 +12% 176 157 EXAMPLE 8 EXPERIMENTAL Ti5 80 120 5.7 2.1 +12% 175 159 EXAMPLE 9 EXPERIMENTAL Ti 10 130 60 5.72.1 FAILURE IN MAKING BATTERY EXAMPLE 10 EXPERIMENTAL Ti 5 130 130 5.72.1 +12% 177 175 EXAMPLE 11 EXPERIMENTAL Al 12 130 60 5.7 2.1 +12% 178175 EXAMPLE 12 EXPERIMENTAL Ti 5 130 60 1.8 2.1 +22% 180 152 EXAMPLE 13EXPERIMENTAL Ti 5 130 60 27 5.7 +21% 178 152 EXAMPLE 14

Among the secondary battery modules including a negative electrodeactive material layer having a laminated structure including a firstlayer containing carbon-based active material particles A with a 10%proof stress of 3 MPa or less and a second layer containing secondcarbon-based active material particles B with a 10% proof stress of 5MPa or greater, such as those in Experimental Examples 1 to 9, asecondary battery module with an elastic body that includes a positiveelectrode collector containing Ti as a main component and having athickness of 1 μm to 8 μm and an elastic body having a compressiveelastic modulus of 5 MPa to 120 MPa exhibits decrease in heat generationtemperature of the battery in a nailing test, as compared with asecondary battery module without an elastic body that includes theabove-mentioned positive electrode collector but does not include theabove-mentioned elastic body. In contrast, a secondary battery modulewith an elastic body that includes an elastic body having a compressiveelastic modulus in excess of 120 MPa, such as in Experimental Example11, does not exhibit substantial decrease in heat generation temperatureof the battery in a nailing test, as compared with a secondary batterymodule without an elastic body.

With a secondary battery module including a negative electrode activematerial layer having a laminated structure including a first layercontaining carbon-based active material particles A with a 10% proofstress of 3 MPa or less and a second layer containing carbon-basedactive material particles B with a 10% proof stress of 5 MPa or greater,such as those in Experimental Examples 1 to 9, the increase rate of aresistance value is small and drop in output of a battery in acharge/discharge cycle is prevented. In contrast, with a secondarybattery module in which the 10% proof stress of the carbon-based activematerial particles A in the first layer does not fall in theabove-described range or the 10% proof stress of the carbon-based activematerial particles B in the second layer does not fall in theabove-described range, such as ones in Experimental Examples 13 and 14,the increase rate of the resistance value is large, and drop of outputof a battery in a charge/discharge cycle is not sufficiently prevented.

REFERENCE SIGNS LIST

-   1 secondary battery module, 2 stacked body, 4 end plate, 6 binding    member, 8 cooling plate, 10 nonaqueous electrolyte secondary    battery, 12 insulation spacer, 13 enclosure, 14 outer can, 16    sealing plate, 18 output terminal, 38 electrode body, 38 a positive    electrode, 38 b negative electrode, 38 d separator, 39 winding core    portion, 40 elastic body, 42 hard portion, 42 a base member, 44 soft    portion, 44 a through hole, 46 recessed portion, 46 a core portion,    46 b linear portion, 50 positive electrode collector, 52 positive    electrode active material layer, 54 negative electrode collector, 56    negative electrode active material layer, 56 a first layer, 56 b    second layer, 58 nail.

1. A secondary battery module, comprising: at least one nonaqueouselectrolyte secondary battery, and an elastic body disposed togetherwith the nonaqueous electrolyte secondary battery, for receiving a loadfrom the nonaqueous electrolyte secondary battery in a direction inwhich the nonaqueous electrolyte secondary battery and the elastic bodyare disposed, wherein the nonaqueous electrolyte secondary batteryincludes an electrode body including a laminate of a positive electrode,a negative electrode, and a separator disposed between the positiveelectrode and the negative electrode, and an enclosure for storing theelectrode body therein, the elastic body has a compressive elasticmodulus of 5 MPa to 120 MPa, the positive electrode includes a positiveelectrode collector containing Ti as a main component and having athickness of 1 μm to 8 μm, the negative electrode includes a negativeelectrode collector and a negative electrode active material layerincluding a first layer and a second layer sequentially formed from aside with the negative electrode collector, and the first layer containsnegative electrode active material particles containing firstcarbon-based active material particles with a 10% proof stress of 3 MPaor less, and the second layer contains negative electrode activematerial particles containing second carbon-based active materialparticles with a 10% proof stress of 5 MPa or greater.
 2. The secondarybattery module according to claim 1, wherein the negative electrodeactive material particles contained in the second layer each have a BETspecific surface area that is smaller than a BET specific surface areaof the negative electrode active material particles contained in thefirst layer.
 3. A nonaqueous electrolyte secondary battery, comprising:an electrode body including a laminate of a positive electrode, anegative electrode, and a separator disposed between the positiveelectrode and the negative electrode, an elastic body for receiving aload from the electrode body in a lamination direction of the electrodebody, and an enclosure for storing the electrode body and the elasticbody therein, wherein the elastic body has a compressive elastic modulusof 5 MPa to 120 MPa, the positive electrode includes a positiveelectrode collector containing Ti as a main component and having athickness of 1 μm to 8 μm, the negative electrode includes a negativeelectrode collector and a negative electrode active material layerincluding a first layer and a second layer sequentially formed from aside with the negative electrode collector, the first layer containsnegative electrode active material particles containing firstcarbon-based active material particles with a 10% proof stress of 3 MPaor less, and the second layer contains negative electrode activematerial particles containing second carbon-based active materialparticles with a 10% proof stress of 5 MPa or greater.